Implementation of the1-Hour Sulfur Dioxide NAAQS

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Discussion of Recent Developments

Chet Wayland and Michael LingU.S. EPA Office of Air Quality Planning and Standards

May 6, 2014

SO2 AREA DESIGNATIONSPart I

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SO2 Area Designations

The challenge: Current scope of SO2 monitoring is limited

Many of the existing monitors are not located to characterize maximum concentrations and source-oriented impactsAdditional monitoring resources are also limitedWhere feasible, it is appropriate for EPA to develop reasonable approaches to determining whether public health is being protected in areas without monitored violationsSome stakeholders have alleged NAAQS violations in certain monitored and unmonitored areas based on modeling they have done

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SO2 Area Designations

The EPA response – after extensive stakeholder consultation SO2 Area Designations & Implementation Strategy

For SO2, appropriate modeling can help meet these challenges. Modeling has been used to characterize air quality for SO2 designations and SIP

adequacy purposes. It allows for characterization of air quality around sources where monitoring is impractical or inadequate

The application of modeling to characterize actual air quality is different from its familiar predictive applications. Actuals based modeling is appropriate for this purpose.

The EPA will identify by rule sources/areas where characterization of air quality is a priority (similar to monitoring network design)

States will characterize these sources using a “dual-pathway” approach (i.e., monitoring and/or actuals modeling)

EPA and States will use this characterization information to complete SO2 designations on an expeditious schedule

This strategy gave rise to the proposed SO2 Data Requirements Rule and the Modeling/Monitoring TADs

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SO2 Data Requirements Rule

Proposed SO2 Data Requirements Rule (DRR) Signed on April 17, 2014; pending FR publication 60 day public comment period (docket EPA-HQ-OAR-2013-0711) Final rule expected in late 2014 Webinar for States coming soon

Elements of the SO2 DRR proposal Expected implementation timeline / deadlines for state submittals Source threshold options Incentives for enforceable emission limits to avoid nonattainment

designation Ongoing assessment of air quality for areas designated

“attainment”

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Expected Implementation Timeline: SO2 DRR Proposal

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Source Threshold Options

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EPA preference is Option 1 “90% emissions” option discussed in May 2012 white paper and stakeholder meetings Minimum monitoring requirement for source-oriented lead NAAQS addresses 90% of the

stationary source emissions Many states supported a threshold of 2,000 tpy 2013 designations generally contain sources above these thresholds No state would have more than 32 sources Close to 10% of the target sources were included in 2013 area designations

Option

ThresholdFor SO2 Sources

Number of Sources**

Percent ofNational

Emissions†

Plus SourcesIn DesignatedNonattainment

Areas‡

Total Source

Coverage

Total Annual EmissionsCoverage

Inside CBSAs Greater than 1M

Outside CBSAs Greater than 1M

1* 1,000 TPY 2,000 TPY 447 75 % 47 496 90 %2 2,000 TPY 5,000 TPY 271 66 % 47 323 82 %3 3,000 TPY 10,000 TPY 159 54 % 47 211 69 %

* Preferred option.** These do not include sources located in nonattainment areas designated in 2013.† Total SO2 emissions in 2011 were 5.8 million tons. ‡ There are 53 sources with annual emissions greater than 1,000 tpy in nonattainment areas designated in 2013.

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Air agencies can avoid nonattainment designation for certain areas by working with sources to establish permanent and enforceable emission limitations that show attainment with the SO2 NAAQS through modeling prior to round of designations in 2017

Emission limits would need to be incorporated into the SIP (e.g. through source-specific SIP/TIP revision, minor NSR permit, consent decree, etc. that gets adopted into the SIP)

Can take into consideration emission reduction measures that will be implemented for Mercury and Air Toxics Standard (MATS) and other rules

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Incentives for Enforceable Emission Limits to Avoid Nonattainment Designation

If areas are designated “attainment” after states provide monitoring or modeling data, states will be required to verify ongoing attainment

Monitors deployed to meet the requirements of this rule in general must continue operation. However, the rule proposes that a monitor may be shut down if it meets certain criteria, including:

Two proposed options: 1. if design value is below 50% of standard; 2. if design value is below 80% of standard.

Modeled areas For other pollutants, monitors are available to track emissions in the

future, but this will not be true for SO2 where state chooses modeling option

Three options are proposed for ongoing assessment of attainment1. Air agency assesses emissions annually, conducts modeling every 3 years2. Air agency assesses emissions annually; if total SO2 emissions increase, air

agency recommends whether more modeling is needed; RA considers case-by-case

3. Air agency conducts screening modeling every 3 years

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Ongoing Assessment of Air Quality for Areas Designated “Attainment”

SO2 Modeling/Monitoring TADs

To assist with the modeling and monitoring called for by the DRR, EPA also issued Technical Assistance Documents for both modeling and monitoring

Key Features: Each TAD provides detailed approaches to characterizing air quality in an area around SO2 emissions sources

These documents have undergone stakeholder review and were posted on the SO2 implementation website on January 7, 2014 for use in commenting on the proposed DRR.

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SO2 Modeling/Monitoring TADs

Modeling TADProvides details on modeling with actual emissions data to provide a design value for an area around emissions sources that is to be used as a surrogate for ambient monitoring dataProvides recommendations on approaches for determining sources to model, meteorological data, and background concentrationsRecommended model in most cases will be AERMODMonitoring TADProvides several approaches on how to determine appropriate locations to monitor for peak, ambient SO2 concentrations around an SO2 emissions source.Approaches include the use of modeling, exploratory monitoring, and weight of evidence approaches to inform monitor placement

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Designations Deadline Suits

The designations timelines using the data from the DRR are expeditious, but the deadline for EPA to complete these designations has already passed.

Deadline suits were filed by Sierra Club/NRDC and several states requesting court to order EPA to issue final designations for all remaining areas with timeframes ranging from a couple months to 2 years from date of order

EPA prefers the orderly approach of the DRR and ensuing designations process and has expressed that in its brief filed April 21, 2013 (in U.S. District Court, Northern District of California).

However, states should be aware that these lawsuits may result in some or all of these designations needing to be done sooner.

In that event, EPA still plans to carry out the DRR to assure air quality is adequately characterized for purposes of designation/redesignation (analogous to monitoring network)

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SO2 ATTAINMENT PLANNINGPart II

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SO2 Attainment Planning

Initial nonattainment area designations, based on violating monitors, were effective October 4, 2013

29 areas in 16 states designated Attainment plans due April 2015; Latest approvable attainment date

October 2018 Judicial challenges filed for three areas designated NA and

regarding EPA’s approach to designations in general

1-hr SO2 NAAQS Nonattainment SIP Elements Guidance

Objective is to provide assistance to areas developing SIPs for current (and future) nonattainment areas

Guidance was issued on April 23, 2014 Webinar for air agencies was held on May 1, 2014

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Key Issues In SO2 Guidance

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Overview of Averaging Time Issue

The new SO2 guidance supports use of averaging times from 1 hr up to 30 days.

Averaging times generally influence the stringency of a limit. Generally, a 30-day average limit is less stringent than a 1-hr limit at the same level.

Once the appropriate 1-hr limit is identified, the guidance advises states wishing to apply a longer term average limit to apply a downward adjustment of the limit, to establish a limit with comparable stringency to the corresponding 1-hr limit that would provide for attainment.

With this downward adjustment of the limit, EPA believes that elevated emissions will be sufficiently rare that violations are very unlikely to occur.

The guidance provides example calculations and discussion of how comparably stringent limits may be determined.

Especially for sources that will use emission control equipment, the guidance also advises adopting supplemental limits to constrain the periods of elevated emissions that can occur with a longer term limit (e.g., requirements for scrubber operation or limits on time and/or magnitude of “emission spikes”)

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Analysis of Averaging Time Approach

Appendix B of the guidance describes analyses conducted to assess air quality impacts of use of long term average limits

EPA analyzed an example facility with two example control strategies One emission data set reflected use of FGD; Other data set reflected low S coal Modeling yielded a critical emission value, then an adjusted 30-day limit was determined using

each emission data set Each emission data set was scaled to just show compliance with the 30-day limit

The FGD run estimated a design value of 46 ppb. The low S coal run estimated a design value of 52 ppb.

Additional analyses, 1) using 100 randomly reassigned emissions data, and 2) using single years of emissions data to characterize emission variability over a 5-year period of meteorology, yielded similar results (50 to 58 ppb in analysis 1, and 39 to 52 ppb in analysis 2)

Appendix C shows sample calculations of adjusted long term limits. Appendix D shows typical EGU adjustment factors

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Clean Data Policy for SO2

Criteria for a “clean data determination” for SO2: (1) Modeling, using actual emissions data, would need to show attainment in the

area and all monitors in the area would need to show attainment, or (2) EPA could use monitoring data alone to determine attainment for an area if the

monitors in the area are determined to be located in the area of maximum concentration.

Regulatory requirements suspended under the “Clean Data Policy”: The SIP requirements that would be suspended under the policy are the following:

RFP Attainment demonstration Contingency Measures

Air agencies would no longer be required to submit the aforementioned SIP requirements “for so long as the affected area continues to attain the standard”

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